The present disclosure relates to a heat pump clothes dryer device and method wherein a circulating fluid exchanges heat with an evaporator. A cool circulating fluid is introduced to a warm humid airflow to condense and collect moisture therein to be returned to the evaporator thereby using the enthalpy of the circulating fluid, evaporator, and dryer airflow.
Conventional clothes dryers generally comprise an open loop air flow passage that introduces hot dry ambient air to a moist load and exhausts the resulting hot humid air to the atmosphere. These dryers have an electric heater to heat the dry ambient air to desired temperatures during a drying process. Additionally, it is known to introduce a continuous flow of cold water to the warm humid air to cause dehumidification of the air prior to being vented to the atmosphere. These dryers often have a very limited drying capacity and also have longer drying cycle times. These dryers also consume large amounts of energy and water during the drying process.
Solutions have been developed to reduce consumption of excess energy and water. One known solution is to circulate the moisture laden air within a closed loop system having a condenser or other heat exchanger. This condenser dryer system uses the condenser to cool the warm humid air and condense water vapor from the warm humid air into either a drain pipe or a collection tank. This air is then reheated at a heat supply and reintroduced to the load again. The heat exchanger typically uses an external ambient air as its coolant. The heat produced by the heat exchanger in this dryer will be transferred to the immediate enclosed surroundings instead of being ducted to an external atmosphere thereby increasing the room temperature. In some designs, cold water is used in the heat exchanger, eliminating this heating, but also requiring increased water usage.
In terms of energy use, condenser dryers typically require less system-wide energy use than conventional dryers. Energy savings result from the associated HVAC system not having to heat or cool additional air to replace that exhausted by the conventional dryer. Typically, this savings is sufficient to offset the increase in power draw, longer drying times, and ambient cooling requirements associated with condensation dryers.
Because the heat exchange process simply cools the internal air using ambient air or cold water, it will not dry the air in the internal loop to as low a level of humidity as the fresh, ambient air. As a consequence of the increased humidity of the air used to dry the load, this type of dryer requires relatively more time than the conventional dryer. Condenser dryers are a particularly attractive option where long, intricate ducting would be required to vent a conventional dryer.
Whereas condensation dryers use a passive heat exchanger cooled by ambient air, heat pump dryers use an internal heat pump having an additional refrigeration cycle. Generally known heat pump dryers help to further reduce energy consumption from the previously mentioned dryer systems. Here, warm humid air from a moist load is passed through a heat pump where the evaporator coil cools the air and condenses the water vapor into either a drain pipe or a collection tank and the hot side reheats the air. Heat pump dryers typically utilize a fin and tube type of evaporator coil within a closed loop air passageway. As with condensation dryers, the known heat exchanger will not dry the internal air to as low a level of humidity as the ambient air.
With respect to ambient air, the higher humidity of the air used to dry the clothes has the effect of increasing drying times. However, because heat pump dryers conserve much of the heat of the air they use, the already-hot air can be cycled more quickly, possibly leading to shorter drying times than conventional dryers. In this way, not only does the dryer avoid the need for external duct routing, but this arrangement also conserves much of the heat within the dryer instead of exhausting the heat into the surroundings. Heat pump dryers can therefore use less than half the energy required by either condensation or traditional dryers.
This arrangement is more efficient than conventional dryers but is susceptible to associated problems of lint accumulation on the evaporator and at times even on the condenser causing lower heat transfer efficiency and difficulty in balancing the sealed system performance during the drying process. Additionally, the continuous change in a cooling load and a dehumidification load further causes inefficiencies with system balance. For at least the foregoing reasons, there remains a need for a more concise, efficient, and cost effective device and method for reducing energy consumption in a heat pump dryer by more efficiently using the enthalpy of a circulating fluid, an evaporator, and air within the device.